This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The dynamic range of luminance in a picture can be defined as a ratio between the highest luminance value of an image and the lowest luminance value of the image:r=bright/dark  (1)where “bright” denotes the highest luminance value of the image and “dark” denotes the lowest luminance value of the image. The dynamic range “r” is generally expressed as a number of power of two, called f-stops or equivalently stops. For instance, a ratio 1000 is about 10 f-stops, which is the typical dynamic range of standard non-HDR videos, also called SDR (Standard Dynamic Range) videos or equivalently LDR (Low Dynamic Range) videos.
Video signals used in the current consumer market are usually represented by 8 bits, and can handle up to 10 f-stops as shown below. An 8-bit video can represent a higher dynamic range than the obvious 8 f-stops if the video signal is not represented linearly but uses a non-linear dynamic compression curve. For instance, applying a BT.709 OETF (Opto-Electronic Transfer Function) curve on a linear light video signal, defined by the ITU-R and approximately equivalent to a gamma (power function) 1/2.2 to 8-bit video signals, would allow a dynamic range of more than 10 f-stops. In particular, the inverse OETF curve is represented as
                    L        =                  {                                                                      V                  4.5                                                                              0                  ≤                  V                  ≤                  0.081                                                                                                                          (                                                                  V                        +                        0.099                                            1.099                                        )                                                        1                    0.45                                                                                                1                  ≥                  V                  ≥                  0.081                                                                                        (        2        )            on the input range V∈ [0,1]. The peak at V=1 outputs the brightest value at L=1, and the lowest non-zero coded value V=1/255 outputs the darkest value at L=0.00087. Thus, the dynamic range for an 8-bit video signal using the OETF curve is r=1/0.00087=1147, roughly 10 f-stops. Since 8-bit video signals can have a dynamic range around 10 f-stops, an HDR video usually refers to a video with a dynamic range noticeably higher than 10 f-stops.
The exact dynamic range that an HDR video application supports may vary. For example, the SMPTE (Society of Motion Picture and Television Engineers) defines a Perceptual Quantizer EOTF (Electro-Optical Transfer Function) also known as PQ EOTF (defined in SMPTE ST. 2084) non-linear transfer curve, preferably coded on 12 bits, which may code the luminance on the range from 0.005 nits to 10000 nits (nit is a term referring to candela per square meter units or cd/m2), leading to a ratio of 2 million or about 21 f-stops. Practically, first deployments of HDR at home may be expected to be TV sets providing not much more than a peak brightness of 1000 nits and a dynamic range of 15 f-stops, preferably on 10 bits data format if possible. This restricted HDR is also referred to as Extended Dynamic Range (EDR). Typically, an SDR video has a bit depth of 8 or 10 bits, and an HDR video has a bit depth of 10 bits and higher. For example, an SDR video can be a 4:2:0 Y′CbCr 10-bit video, and an HDR video can be a PQ OETF Y′CbCr 12-bit video.